During designing of a rotary USB interface data card, one of the essential factors for determining of low frequency indices of OTA (Over The Air) is to ensure good performance of the rotary USB interface. The connection ability of a wireless device to a network and the effect of a wireless device user on radiation and reception performance can be verified by an OTA test, and the OTA indices contain TRP (Total Radiated Power) and TIS (Total Isotropic Sensitivity). TRP evaluates radiation performance of the wireless device, and a greater TRP value indicates a better radiation performance of the wireless device. TIS evaluates reception performance of the wireless device, and a smaller TIS value indicates a better reception performance of the wireless device.
FIG. 1 is a 3D exterior view of a conventional rotary USB interface data card, in which the USB part can rotate about the PCB (Printed Circuit Board) part.
FIG. 2 is a top view of a rotary USB interface data card with a conventional grounding manner. FIG. 3 is a side view of the data card shown in FIG. 2. FIG. 4 is a 3D schematic view of the data card shown in FIGS. 2 and 3, including a partial enlarged view of a rotary part. With reference to FIGS. 2, 3 and 4, a grounding path of the data card mainly includes a ground wire 20 in the USB 10, a rotary shaft 30 in contact with the ground wire 20, a spring tab or presser tab 40 in contact with the rotary shaft 30, a ground wire 50 in a FPC (Flexible Printed Circuit) board or a cable, and an exposed copper covering grounding region 60 on a PCB 70 in connection with the spring tab or presser tab 40.
Generally speaking, the width of the ground wire 20 of the USB 10 and the width of the ground wire 50 in the FPC or cable are controlled by the size of the overall structure of the data card, and the rotary shaft 30, the spring tab or presser tab 40 and the copper covering grounding region 60 are connected with each other in generally a point contact manner, which lower the grounding performance of the data card. When OTA test is performed on the rotary USB interface data card in the relevant art, it is found that its TRP/TIS indices are relatively poor in the case of 800 MHz and 900 MHz. It can be seen that the grounding performance of the rotary USB interface data card directly affects the OTA low frequency indices of the antenna 80.
To enhance the grounding performance of the rotary USB interface data card, the structure of the rotary USB interface data card may be improved. FIG. 5 is a top view of an improved rotary USB interface data card in the relevant art, FIG. 6 is a side view of the data card shown in FIG. 5.
From the structure of the data card shown in FIG. 5 and FIG. 6 where the grounding manner is improved, it can be seen that:
The improved rotary USB interface data card shown in FIG. 5 and FIG. 6 introduces a shield cover 90, a conductive foam 102, a data card housing 103, and a conductive paint layer 101 sprayed on part of the data card housing 103, besides those components shown in FIG. 2. There exists in the improved data card a large connection area between the spring tab or presser tab 40 and the shield cover 90 via the conductive paint layer 101 and the conductive foam 102, forming a grounding loop, which somewhat improves the grounding effect of the data card itself, but the improved effect is not enough for the desired grounding performance of the data card. The OTA indices of the data card remain relatively poor and also the transmitting/receiving performance is not satisfactory. Furthermore, there still exists some defects in such a data card structure: on the one hand, the use of the conductive paint layer and the conductive foam increase the production cost of the data card; on the other hand, the introduction of the extra components results in complication of production process of the data card.